To reduce discharge of fuel vapors into the atmosphere, motor vehicles induct fuel vapors from a fuel tank into the engine. An evaporative emission control system including a carbon canister is also coupled to the fuel tank to adsorb fuel vapors under some conditions. For example, the carbon canister may adsorb refueling, diurnal and running loss vapors. The carbon canister, however, has limited capacity, thus engine running manifold vacuum may be used to desorb the vapor from the carbon canister via opening of a purge valve. Desorbed vapors are combusted in engine.
Fuel tanks in such vehicles may include a fuel level sensor within the fuel tank for determining an amount of fuel in the fuel tank so that, for example, an operator of the vehicle may be alerted to refuel the vehicle when the fuel level is low, e.g., below a threshold value. For example, during refueling, the fuel level sensor may be used to determine how much fuel was added to the fuel tank so that indications of fuel level may be adjusted accordingly.
However, the inventors herein have recognized that fuel level sensors in the fuel tank may be inaccurate during certain conditions, e.g., when a vehicle is parked on an uneven surface or on an incline. Further, fuel level sensors in a fuel tank may become degraded over time so that such sensors provide unreliable or inaccurate indications of fuel level. Thus, the inventors herein have recognized that it may be desirable to provide a secondary or backup fuel level sensing approach to infer fuel amount in the tank.
Further, the inventors herein have recognized that during a refueling event an exothermic reaction associated with vapor adsorption in the canister takes place leading to an increase of temperature in the canister. As more fuel is dispensed into the fuel tank, portions of the canister may become saturated so that the vapor flowing through the canister cools the adsorbent in the canister leading to a decrease in temperature in the canister. Further, at the end of refueling, vapor diffusion from downstream portions of the adsorbent in the canister causes a heating effect wherein the temperature again increases in the canister. The inventors have recognized that such temperature changes in the canister may be used to infer a fuel level of the tank. This fuel level may be adjusted to obtain a current fuel level by taking into account how much fuel is injected into the engine during engine operation to that the amount of fuel in the tank may be tracked and indicated accurately.
In one example approach, a method for an engine with an evaporative emission control system comprises, indicating a fuel level in a fuel tank based on a temperature change of adsorbent in a carbon canister during refueling. In some examples, the temperature change may be based on a cool down duration based on a single temperature sensor coupled to the canister. In other examples, the temperature change may be based on a plurality of temperature sensors coupled to the carbon canister at various depths.
In this way, a secondary source for fuel level indication, instead of or in addition to a fuel level sensor in the fuel tank, may be provided to accurately determine fuel levels in a fuel tank by inferring a fuel level based on temperature changes in the canister. Such an approach, may increase accuracy of fuel level determination and reduce errors associated with fuel level sensors inside the fuel tank. Further, in some examples, a single temperature sensor in the canister may be used to monitor temperature changes to infer fuel level which may lead to increased fuel level accuracy with minimal additional costs.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.